The invention relates to a method and device for controlling the drive train of a motor vehicle.
WO 97/01049 disclosed a hydrostatic mechanical power split gear whose ratio is continuously variable without interrupting the traction force or the thrust (power shift gear). A mechanism power branch and a hydrostatic power branch are driven by a common input shaft and summed in a coupled gearing. The coupled gearing contains several planetary gear sets. The output of the planetary gear is connected with a reversing gear and can optionally be connected via a clutch Kv for forward motion or clutch Kr for reverse motion, and the reversing gear with the output shaft. With the power split gearing known already, a motor vehicle can be reversed at low speeds via the clutches Kv and Kr, i.e. its travel direction can be reversed. This means, for example, that the clutch Kr can already be closed with pressure modulation when the vehicle is still moving forward. Starting from a specific modulation pressure, the clutch Kv previously closed, can be opened and the forward moving vehicle decelerated via the clutch Kr until stopping, and then accelerated in reverse direction of motion. The actually adjusted gear ratio remains constant during the reversal operation. It is only changed again after the reversal via the clutches Kv/Kr is terminated. Thereby can be obtained with satisfactory shifting comfort quick reversals of travel direction without interrupting the traction.
In a drive train of a motor vehicle which has a transmission with continuously variable ratio and shiftable clutches for reversing the travel direction, the invention solves the problem by providing a possibility by which at vehicle speeds higher than in the prior art a reversal of travel direction can be automatically started after the driver has selected on a control device such a reversal of travel direction without the clutches being quickly worn or destroyed, or substantially larger clutches or a larger transmission than in the prior art being required. In addition, a jerk-free driving operation is ensured even during reversal of travel direction.